D0ctor Fantastic is extremely arrogant and will do anything to prove that he's right and that his opponent in an argument is wrong. In fact, this is what brought him to New Mario's era in the first place, since he traveled back in time to kill Pinkie Pie after he got in an argument with her over whether she started the war. Despite this, he is rather self-sacrificing, perhaps almost stupidly so, as he insists on winning the argument despite doing so inevitably leading to his non-existence.